std::ranges::destroy_at

 

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Defined in header <memory>
Call signature
template< std::destructible T > constexpr void destroy_at( T* p ) noexcept;		(since C++20)

If T is not an array type, calls the destructor of the object pointed to by p, as if by p->~T(). Otherwise, recursively destroys elements of *p in order, as if by calling std::destroy(std::begin(*p), std::end(*p)).

The function-like entities described on this page are niebloids, that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

p

-

a pointer to the object to be destroyed

Return value

(none)

Possible implementation

struct destroy_at_fn { template<std::destructible T> constexpr void operator()(T *p) const noexcept { if constexpr (std::is_array_v<T>) for (auto &elem : *p) operator()(std::addressof(elem)); else p->~T(); } };   inline constexpr destroy_at_fn destroy_at{};

Notes

destroy_at deduces the type of object to be destroyed and hence avoids writing it explicitly in the destructor call.

When destroy_at is called in the evaluation of some constant expression e, the argument p must point to an object whose lifetime began within the evaluation of e.

Example

The following example demonstrates how to use ranges::destroy_at to destroy a contiguous sequence of elements.

Run this code

#include <iostream>
#include <memory>
#include <new>
 
struct Tracer
{
    int value;
    ~Tracer() { std::cout << value << " destructed\n"; }
};
 
int main()
{
    alignas(Tracer) unsigned char buffer[sizeof(Tracer) * 8];
 
    for (int i = 0; i < 8; ++i)
        new(buffer + sizeof(Tracer) * i) Tracer{i}; //manually construct objects
 
    auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));
 
    for (int i = 0; i < 8; ++i)
        std::ranges::destroy_at(ptr + i);
}

Output:

0 destructed
1 destructed
2 destructed
3 destructed
4 destructed
5 destructed
6 destructed
7 destructed

See also

ranges::destroy (C++20)	destroys a range of objects (niebloid)
ranges::destroy_n (C++20)	destroys a number of objects in a range (niebloid)
ranges::construct_at (C++20)	creates an object at a given address (niebloid)
destroy_at (C++17)	destroys an object at a given address (function template)